1. Field of the Invention
The present invention relates to a device for manufacturing lubricant supply grooves in a fluid bearing in which high speed rotation with high precision is required. More particularly, the invention relates to a device for manufacturing lubricant supply grooves in a fluid bearing in which a working portion is replaceable when it becomes worn, and a number of lubricant supply grooves of a spiral or circular type, can be formed at one time.
2. Description of Related Art
A head drum assembly of a tape recorder such as a video tape recorder (VTR) or a digital audio tape (DAT) recorder requires high speed rotation with high precision, so as to record/reproduce a tape having a high density format. Thus, a ball bearing is disposed between the head drum and the rotation axis, for providing a friction-reduced rolling interface. However, since the head drum assembly utilizing a ball bearing requires space for accommodating the ball, the assembly increases in size, and noise is generated due to a gap required for the ball's rolling motion. Also, rotation accuracy is lowered due to wear on the ball.
Thus, recently, lubricant supply grooves have been formed wherein fluid flows along the inner wall of the sleeve, and a high speed and high precision fluid bearing has been used for reducing the fluid friction between the rotating axis and the sleeve.
A conventional manufacturing device used for the formation of such lubricant supply grooves is shown in FIG. 1. A number of holes are formed on the outer circumferential surface of tool body 1. A ball 4 is inserted from the interior of tool body 1 into respective holes. A support 3 is fitted into the interior of tool body 1 so as to support ball 4. Here, since the diameter of the hole is smaller than that of ball 4, the latter is held within tool body 1.
The lubricant supply groove manufacturing device as described above is used in the following manner. A sleeve 2 is fixed with a chuck (not shown). When pressure is exerted on tool body 1 to advance it in the axial direction of sleeve 2, the inner wall of sleeve 2 is plastically deformed so that supply grooves 5 are formed. If the chuck is also rotated while exerting pressure on tool body 1 to advance it in the axial direction of sleeve 2, the lubricant supply grooves 5 formed on the inner wall of sleeve 2 may be spirally shaped. Accordingly, various types of lubricant supply grooves 5 may be formed in accordance with the rotating condition of the chuck.
However, during plastic processing work, ball 4 and support 3 can become worn or deformed due to friction between the inner wall of sleeve 2 and ball 4. Accordingly, supply grooves 5 are not uniformly manufactured, thereby lowering the bearing performance. Thus, a worn ball 4 must be replaced. As shown in the drawing, in the conventional lubricant supply groove manufacturing device, since a number of balls 4 are inserted into respective holes from the interior of tool body 1, and each is supported by support 3, replacement is difficult. Thus, the tool is not highly efficient.
Also, because of practical limitations it is very difficult to manufacture and manipulate very small balls. Accordingly, certain desirable formations of very small lubricant supply grooves 5 cannot be provided with the above-described conventional device.